Friction bonding of hard-to-grip workpieces

ABSTRACT

A process for friction or inertia bonding difficult-to-grip parts wherein the parts are mounted within fixtures and a lowmelting-temperature alloy is poured into the fixtures so as to absorb hoop stresses and to prevent relative rotation between the workpiece and the fixture.

[56] References Cited UNITED STATES PATENTS Inventors Robert C. Barth Peoria; Marion R. Calton, East Peoria; Daniel L.

United States Patent Primary Examiner-John F. Campbell Assistant ExaminerRobert J. Craig Attorney-Fryer, Tjensvold, Feix, Phillips & Lempio process for friction or inertia bonding difficult-to-grip parts wherein the parts are mounted within fixtures and a low-melting-temperature alloy is poured into the fixtures so as to absorb hoop stresses and to prevent relative rotation between the workpiece and the fixture.

29/470.3, ABSTRACT: A ,l56/73, 164/90, 228/2 [51] 228/2;

Peoria, lll.

WORKPIECES 6 Claims, 9 Drawing Figs. [52] 29/423 %3RX 3 0 3 00 q7mm2fl77 m m mm 9 9 99 2 2 22 m m Tm m m m 1 t e mm w NW N ywb n. r. uoeOa PHFRHGC 46800999 6666666 9999999 1111111 2795 2 11 002 300 3 96 M4 4 85394005 399478 3333333 e m m mm E m n o C u r m m .,e mum mm. I 9 Pnmmmflm mmmafim KWP7&MC 0 8 N mm L n wmmm AHPA llll I253 224- [[[i 541 FRICTION BONDING 0F HARD-TO-GRIP PATENTEDMAR23|97| 3571.906

' SHEET2UFf4 a INVENTORS ROBERT C. BARTH MARION R. CALTON DANIEL L. KING THEODORE L. OBERLE FRANKLIN E. ZIMMERMAN BY I w IW Q ATTORNEYS PATENT Etj l unzal sr l sum 3 or 4 INVENTORS.

ROBERT C. BARTH MARION R. CALTON DAN THEO FRA IEL L. KING DORE' L. OBERLE NKLlN E. ZIMMERMAN j'fiiw "1'47" ATTORNEYS PATENTEB mm R 315-71} 906 SHEET u 0P4.

37-; E 3" & -I-5 33 INVENTORS ROBERT C. BARTH MARION R.CALTON DANIEL L. KING THEODORE L. OBERLE FRANKLIN E. ZIMMERMAN BY. 9- Z 145 I ATTORNEYS ERECTION BONDING OF IIAlRD-TO-GQIIP WORKIIIECIES This invention relates to the inertia welding of parts which are difficult to grip, such as turbine engine rotor assemblies, and to a method of welding such parts. While the following description will be directed toward the welding of turbine engine rotor assembly, it should be home in mind that these specific assemblies are being utilized for descriptive purposes only and that many such assemblies may be similarly welded by the techniques herein disclosed.

Although it has not been easy to weld parts which are difficult to grip due to problems of tolerance and relative fragility, such problems have taken on a greater significance recently due to the emphasis now being placed upon the production of gas turbine engines for commercial use.

In a gas turbine engine, it is desirable to have a rotor which is economical, dependable, safe, and capable of withstanding extreme operating conditions for an extended period of time. In forming such a rotor, it is highly desirable to have a blade ring which will withstand extremely high temperatures and a disc and hub section which are of ductile material capable of withstanding high stresses.

When the entire rotor is cast from a high temperature alloy material which will withstand the high temperatures which the blades must endure, the hub has a lack of strength and ductility and becomes a hazard to safety due to the possibility of rotor rupture.

One method of producing a composite rotor assembly is to utilize a ductile hub and attach individual blades of a high temperature alloy material to the hub.'The blades are usually attached to the hub by a fir tree construction method and the parts are held together mainly through a friction and mechanical locking means. Such a fir tree assembly can be seen in US. Pat. No. 3,104,093 to Craig, et al.

Since the advent of commercial usage of inertia and friction welding-described in US. Pat. No. 3,273,233 to Oberle, et al.attempts have been made to weld composite rotor assemblies by such processes. In performing such welds, boltholes were provided in the blade ring so as to hold it to the welding fixtures. This method proved to be unsatisfactory, however, in view of the fact that the boltholes created points of weakness within the blade rings leading to the possibility of rupture thereof.

When the stresses that are developed in the weld pieces during the welding operation are calculated, it is shown that the tangential stress, welding torque required, and axial welding load required to achieve the desired weld interface pressure are all dependent on the weld angle. As the angle is increased in size, the weld area is increased, and a larger energy and axial load input is required, thereby increasing the torque necessary to perform the weld.

Additionally, the weld angle relationship must be determined in light of the linear expansion of the two workpieces during the operation of the gas turbine engine since the rela tive thermal expansion therebetween may cause twisting or distortiona fault which is critical in a gas turbine engine. In generm it can be stated that the larger the weld angle that is used, the greater amount of relative thermal expansion produced. Thus, it can be seen that the weld angle should be as small as possible-a directly contrary requirement to that found in hoop stress minimization.

In order to provide the optimum weld angle between the workpieces, the angle may be held to a relatively small angle by providing a reinforcing band about the blade ring in order to contain the hoop stresses during welding. The reinforcing band may be formed by use of a low melting temperature alloy to fill the area between the blades, thereby containing the hoop stresses which otherwise might deleteriously affect the relatively fragile blades and blade ring.

It is therefore an object of this invention to provide a means for forming bonds between materials having varying properties.

It is also an object to provide a method and apparatus for bonding metalic parts when at least one of the workpieces is difficult to hold during the bonding process.

It is also an object of this invention to provide a method of forming a temporary reinforcing band on a workpiece so as to facilitate the welding of such a workpiece.

It is a further object of this invention to provide a temporary reinforcing band upon a workpiece so as to obviate the effects of hoop stresses upon such workpiece during high-speed rota tion thereof.

It is still a further object of this invention to provide a method and apparatus for forming such a reinforcing band which also prevents relative rotation between the workpiece and its holding fixture.

It is also an object of this invention to provide a method and means for forming a high-speed turbine rotor wheel.

Other objects and advantages of the present invention will become apparent from the following description and claims as illustrated in the accompanying drawings which, by way of illustration, show a preferred embodiment of the present invention and the principles thereof and what is now considered to be the best mode contemplated for applying those principles. It is recognized that other embodiments of the invention utilizing the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and purview of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a side elevation illustrating one embodiment of a friction or inertia welding machine which may be utilized to practice the methods of the present invention;

FIG. 2 is a cross section of a welded turbine rotor assembly;

FIG. 3 is a front view of a blade ring holding fixture suitable for holding a rotating weld piece;

FIG. 4 is a side sectional view of the blade ring holding fixture taken along a line lV-IV of FIG. 3;

FIG. 5 is a front view of a rotor hub holding fixture suitable for holding a stationary weld piece;

FIG. 6 is a side sectional view of the hub holding fixture taken along a line VI-VI of FIG. 5;

FIG. 7 is a view of the fixture side of a welded rotor assembly with the reinforcing band about the blade;

FIG. 8 is a side sectional view of the assembly of FIG. 7 taken along a line VIII-VIII thereof; and

FIG. 9 is a view of the assembly of FIGS. 7 and 8 taken along a line IX-IX of HO. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENT A friction welding machine constructed so as to produce the weld described herein is indicated generally by the reference numeral lit) in FIG. I. As shown, the machine comprises a frame or housing structure generally denoted at E2 for housing the various elements of the machine. The two workpieces to be welded, WP-ll and WP-Z, are mounted within chucks i4 and to.

The chuck to does not rotate and is mounted on a tailstock fixture lb. The fixture I8 is mounted for axial movement of the machine frame 12 under the control of a load cylinder 26. A pressure control circuit (not shown) regulates the pressure in a load cylinder, and thus determines the axial force with which the workpieces are engaged.

The chuck M is mounted on a spindle 22 and the chuck and spindle are mounted for rotation within the frame 12. The rotary spindle 22 is adapted to receive flywheels 24 which may be of various size and mass depending upon the particular application of the machine.

An electric motor 26 rotates the spindle through a hydrostatic transmission indicated generally by the reference numeral 28. The transmission includes hydrostatic pump 36', a hydrostatic motor 32, and a manifold Eidbetween the pump and motor.

The drive ratio between the motor and the spindle 22 can be varied by changing the cam angles in either the pump 36 or the motor 32, and the pump and motor can be used to effectively disconnect the motor 26 from the spindle 22 by moving the cam of the pump 30 to a position in which the pump does not displace any hydraulic fluid to the motor 32.

It is to be understood that the flywheel weights 24 are mounted on the spindle 22 so that the welding machine can be operated in the manner described in US. Pat. No. 3,273,233 and is described in further detail below.

A welding operation to join a first workpiece to a second workpiece can be performed by operating the machine in the following general manner.

One of the workpieces, WP-l, is firmly clamped in the rotatable chuck 14 located on the spindle 22. The other workpiece WP-Z is firmly clamped in the nonrotatable chuck 16 which is located on the tailstock portion 18 of the machine. Upon actuation of the motor 26, the flywheel and workpiece -WP-i are accelerated to a predetermined velocity.

Once this velocity has been obtained, the motor 26 is disconnected or shut down and the ram mechanism 20 is actuated to move tailstock portion 18 and workpiece WP-Z axially into contact with the rapidly rotating workpiece WP-l. As the two workpieces are brought into contact under the upsetting pressure applied through ram 29, heat is generated at the contacting surface or interface of the weld piece. This heating increases until the workpieces reach the weld temperature, at which time the upsetting pressure, applied by the ram 20 at either a constant or varying pressure, causes flashing or upsetting to occur. During this heating and flashing, the rotational velocity of the spindle 22 continues to decrease. At the time the rotation of the spindle ceases, upsetting has taken place and the weld is completed.

Although the above-described use of the machine of FIG. 1 is that of inertia welding, it is not intended to limit this invention to an inertia welding process only, but rather to include the processes of friction welding as described in Friction Welding of Materials" by V. l. Vill, published by-American Welding Society, inc. New York, Library of Congress Catalog Qard Number 62-13420.

As previously mentioned, one of the problems associated with the friction welding of a blade ring to the hub is that of holding the blade ring without damaging any of the blades. As shown in FIG. 2, the rotor blades 11 in the most economical rotor manufacture are integral with the blade deck 13 which must be suitably attached to the hub at the interface 17. Blade ring 13 is normally a cast alloy and the hub 15 is normally of a wrought material. The angle at interface 17 has been illustrated as being 30, but it may be varied depending upon the maximum allowable hoop stresses and the other usual welding parameters.

It has been found that the solution to the problem of holding the blade ring during welding is to fill the area between the individual blades with a low melting point alloy, for example, a bismuth alloy such as Cerromatrix. The blade then becomes a solid ring which is able to withstand any stresses incurred during the welding.

In FIGS. 3 and 4 a holding fixture 21 is illustrated which will be suitable for carrying the blade ring in rotation during the welding process.

In use of this fixture, blade ring 13 is inserted in an aperture 23 in the fixture and the liquified alloy is poured over the blades around the periphery of the aperture. In order to keep the blade ring from turning and also to resist the high torque developed during welding of the blade ring to the hub, a plurality of recesses 25 are machined into the holding fixture and are separated by ribs 27. As the alloy is poured over the blade structure, these recesses become filled at the same time that the area between the blades is filled, thereby forming a connection between the fixture and the blade ring. Referring to FIGS. 7 and 8, it can be seen that the alloy forms a set of teeth 31 separated by grooves 33 throughout the periphery of the blade ring as it hardens about ribs 27 in the apertures 25 of the fixture.

In this way, the resultant torque is transferred from the blade rings to the fixture 21, with the ribs 27 preventing the blade ring from turning within the fixture during welding. The

deck 41 of the blade n'ng rests against a ring 43 of the fixture so that the axial force applied during welding is transmitted to the welding fixture.

Fixture 21 may then be fixed to the rotatable chuck 14 by suitable means such as boltholes 45.

A hub holding fixture 51 is illustrated in FIGS. 5 and 6. The fixture, which is mounted on the nonrotatable chuck 16 by means such as boltholes 53, is machined with two hexagonal pilots 55 and 57 to hold the mating hexagons 61 and 63 respectively, of hub member 15, as shown in FIGS. 7 and 8. The double hexagon on the hub prevents the hub from turning during welding and also resists the torque which is developed during the welding operation.

Use of the fixtu'res 21 and 51 forming a suitable weld at interface 17 between the blade ring and the hub may be illustrated as follows. The required amount of energy to make the weld must be calculated in a known fashion, and the proper flywheel 24 attached to the welding machine 10. The proper speed setting for the selected flywheel is then preset on the machine, as is the pressure to be exerted by ram 20.

Blade ring 13 is then placed in aperture 23 of fixture 21 with deck 41 resting on ring 43. The heated alloy is then poured about the blade ring so that it fills apertures 25 forming ridges 33 over ribs 27 and surrounds the blades.

While the potting material is hardening-a matter of minutes-hub member 15 is fitted into fixture 51 such that the hexagonal portions 61 and 63 thereof mate with the hexagonal apertures 55 and 57 of the fixture.

The blade ring fixture 21 is mounted on rotatable chuck 14 and the hub fixture 51 is mounted on the nonrotatable chuck 16. The weld members are then welded at interface 17 in the previously described manner.

The welded rotor is then removed from the machine and the low melting alloy is melted away from the rotor without harming the assembly.

Thus, the applicants have disclosed an improved method and apparatus for welding structures which are difficult to grasp without being damaged while reducing the hoop stress effect.

While the illustration and description have shown a preferred embodiment of the invention and only a single application thereof, it is to be understood that these are capable of variation and modification, and therefore the invention is not to be limited to the precise details set forth above but rather is to include such changes and alterations as fall within the purview of the following claims.

We claim:

1. A method of bonding metal workpieces comprising the steps of:

a. mounting a first workpiece in a first holding fixture;

b. placing a second workpiece in a second holding fixture;

c. pouring a low melting temperature alloy about at least one of said workpieces in its respective holding fixture, thereby forming a cooperative retaining surface between that workpiece and its fixture;

d. allowing said alloy to solidify;

e. relatively rotating said workpieces at a predetermined speed;

f. bringing said workpieces into contact to generate heat;

and

g. exerting an axial force in the direction of the contacting workpieces.

2. The method of claim 1 wherein said step of relatively rotating said workpieces while exerting a relative axial force therebetween occurs while friction-welding said workpieces.

3. The method of claim 1 wherein said step of relatively rotating said workpieces while exerting a relative axial force therebetween occurs while inertia-welding said workpieces.

4. The method of claim 1 further including the steps of allowing the workpieces to cease their rotating and then heating said alloy and thereby removing it from the welded assembly.

5. A method of bonding metallic parts at least one of which have shape which is difiicult to grip comprising the steps of:

placing one part in a cavity of a holding fixture;

al from the assembly.

6. The method of claim 5 wherein said one part is a turbine rotor blade ring and said step of filling said cavity includes the step of filling of the area between the blades of said blade ring with said liquified material, thereby forming a solid ring capable of withstanding hoop stresses created during the step of rotating the parts. 

1. A method of bonding metal workpieces comprising the steps of: a. mounting a first workpiece in a first holding fixture; b. placing a second workpiece in a second holding fixture; c. pouring a low melting temperature alloy about at least one of said workpieces in its respective holding fixture, thereby forming a cooperative retaining surface between that workpiece and its fixture; d. allowing said alloy to solidify; e. relatively rotating said workpieces at a predetermined speed; f. bringing said workpieces into contact to generate heat; and g. exerting an axial force in the direction of the contacting workpieces.
 2. The method of claim 1 wherein said step of relatively rotating said workpieces while exerting a relative axial force therebetween occurs while friction-welding said workpieces.
 3. The method of claim 1 wherein said step of relatively rotating said workpieces while exerting a relative axial force therebetween occurs while inertia-welding said workpieces.
 4. The method of claim 1 further including the steps of allowing the workpieces to cease their rotating and then heating said alloy and thereby removing it from the welded assembly.
 5. A method of bonding metallic parts at least one of which have shape which is difficult to grip comprising the steps of: placing one part in a cavity of a holding fixture; filling the rest of said cavity, without covering the bonding face of said part, with a liquified low melting temperature material to lock the part to the fixture as the material solidifies; allowing said moisture to solidify; and pressing the parts together and rotating them in rubbing contact until they are bonded together and rotation is stopped, and subsequently removing the solidified material from the assembly.
 6. The method of claim 5 wherein said one part is a turbine rotor blade ring and said step of filling said cavity includes the step of filling of the area between the blades of said blade ring with said liquified material, thereby forming a solid ring capable of withstanding hoop stresses created during the step of rotating the parts. 